1. Field of the Invention
The present invention relates to a magnetic recording/reproducing device including a speed reducer for driving a mechanism section of the magnetic recording/reproducing device which is provided with a worm gear and a worm gear bearing for defining the position of the worm gear.
2. Description of the Related Art
Recently, speed reducers for use in a magnetic recording/reproducing device are beginning to use less (operational) parts so as to realize reduction in size and production cost of the magnetic recording/reproducing device. In order to provide a speed reducer which maintains a high speed reduction ratio while using a small number of parts, it is necessary to provide a worm gear in the speed reducer. The worm gear, as commonly known in the art of magnetic recording/reproducing devices, maintains a high speed reduction ratio by shifting a gear down to a speed of a next lowest gear.
A speed reducer of a conventional magnetic recording/reproducing device will now be described.
FIG. 4 is a structural view showing a loading motor section of a speed reducer 400 of a conventional magnetic recording/reproducing device. FIG. 5 is a magnified view of a thrust bearing of the conventional speed reducer. FIG. 6 is a view for explaining the shape and size of the conventional thrust bearing.
In FIG. 4, the speed reducer 400 includes a loading motor 1, a loading motor shaft 1a, a holder 2, a worm gear 3 and a worm gear bearing 4. The loading motor 1 is coupled to the loading motor shaft 1a so as to rotate the loading motor shaft 1a about a dotted line denoted by reference numeral 401 (hereinafter, referred to as the “rotation center line 401”). The loading motor shaft 1a receives rotation output provided by the rotation of the loading motor 1. The holder (holder section) 2 holds and defines a position of the loading motor 1 within a chassis (not shown) in which the loading motor 1 is mounted. The holder 2 has a retaining member 2a for holding and retaining the loading motor 1 in the position defined by the holder 2 so as to prevent the loading motor 1 from being separated from (i.e., falling out of) the holder 2. The worm gear 3 is coaxially provided on the loading motor shaft 1a. The worm gear bearing 4 is integrally formed with the holder 2. The worm gear bearing 4 receives a worm gear tip 3a and defines a position of the worm gear 3 for reliable and effective operation thereof.
The operation of the conventional speed reducer 400 of the conventional magnetic recording/reproducing device is described below.
Referring to FIG. 4, the loading motor shaft 1a is rotated by applying a voltage to the loading motor 1. This rotates the worm gear 3 coaxially provided on the loading motor shaft 1a. The worm gear 3 transmits the rotation to a worm wheel (not shown) which is a speed reduction element coupled to the worm gear 3. By this mechanism, the rotation of the worm gear 3 is transmitted to other operational elements included in the speed reducer, thereby driving a mechanism section of the conventional magnetic recording/reproducing device. A specific description of this rotation transmission is omitted herein for brevity.
Next, operation of the conventional thrust bearing (i.e., worm gear bearing 4) is described. The (rotation) force transmitted to the worm gear 3 causes the worm gear 3 to be inclined to move along a thrust direction thereof (i.e., downward with respect to the plane of FIG. 4, and more specifically along a direction of the rotation axis of the worm gear 3) by degrees of a torsion angle of the worm gear 3. This force is denoted by F shown in FIG. 4. The worm gear bearing 4 receives force F applied by the worm gear 3.
Referring to FIG. 5, the relationship between force F3 applied by the worm gear 3 to the worm gear bearing 4 and force F4 applied by the worm gear bearing 4 to the worm gear 3 in response to force F3 is described.
In FIG. 5, reference numeral 4a denotes the position of the worm gear bearing 4 before the loading motor 1 is assembled into the holder 2, and reference numeral 4b denotes the position of the worm gear bearing 4 after the loading motor 1 including the worm gear 3 provided on the loading motor shaft 1a is assembled with the holder 2. In this case, deflection of the worm gear bearing 4 amounts to distance D shown in FIG. 5, and force F4 generated by the worm gear bearing 4 is determined from deflection D.
When the force applied by the worm gear 3 to the worm gear bearing 4 along the thrust direction thereof is represented by F3, force F4 applied by the worm gear bearing 4 to the worm gear 3 in response to force F3 is required to be equal to or more than force F3 in order to maintain a suitable position of the worm gear 3 on the worm gear bearing 4 so that the worm gear bearing 4 defines a suitable position of the worm gear 3 for reliable and effective operation thereof. A relationship between force F4 and force F3 is represented by F4≧F3.
In the case where forces F3 and F4 have the above relationship, when the worm gear 3 is rotated, movement of the worm gear 3 along the thrust direction thereof does not occur, and thus the rotation of the worm gear 3 is stabilized. Further, load applied to the worm gear 3 and noise, which are produced during the rotation of the worm gear 3, are reduced.
Force F4 generated by the worm gear bearing 4 is determined by the shape, i.e. length L, thickness T, and width W shown in FIG. 6, of the worm gear bearing 4 and deflection D shown in FIG. 5 thereof.
However, in the conventional speed reducer 400, it is difficult to determine these parameters for setting for force F4 generated by the worm gear bearing 4 so as to stabilize the rotation of the worm gear 3 under the above-described condition. Specifically, as magnetic recording/reproducing devices become more compact, there is difficulty in increasing a two-dimensional size, i.e., the length L, width W, etc., of the worm gear bearing 4. Further, if the worm gear bearing 4 is excessively deflected so as to maintain force F4 which is a load, the worm gear bearing 4 undergoes rupture or permanent deformation, and thus deflection D cannot be increased so as to accommodate the necessary force F4. Furthermore, if the thickness T of the worm gear bearing 4 is increased so as to maintain force F4, the position of the worm gear 3 is not settled (stable), so that variance in force F4 becomes greater as the thickness T of the worm gear bearing 4 becomes greater. Further still, if the size of the holder 2 for holding the loading motor 1 is increased to increase force F4, then the effect of providing a compact magnetic recording/reproducing device is lost. If deflection D and the thickness T are further increased, the worm gear bearing 4 undergoes creep deformation under high temperature environments which occur in operation of the magnetic recording/reproducing device, causing a reduction in force F4. In order to solve this problem, it is necessary to increase the length L, decrease deflection D, or increase the overall size of the worm gear bearing 4. Alternatively, it is necessary to select an expensive creep-resistant material for or provide an additional element to the worm gear bearing 4.